1. Field of the Invention
By present invention relates to an apparatus for measuring dimensions, in particular diametral and axial dimensions of parts with rotational symmetry arranged on a support, with a support structure, a system of slides with a first slide movable with respect to the support structure along a longitudinal axis and a second slide movable along a transversal direction, transducer means adapted to provide signals responsive to the positions of the sides, measuring means carried by the system of slides, and processing means adapted to receive the signals of the transducer means and the signals of the measuring means for combining them. This apparatus will be referred to herebelow as the apparatus of the type set forth.
2. Description of the Prior Art
Automatic gauging machines, or multidimensional gauges are known, for example from U.S. Pat. No. 3,889,380, that substantially comprise a support, a certain number of heads for comparative measurement fixed to the support in a rigid or to certain extent adjustable way, and datum means for positioning the part to be checked. Every measuring head has movable arms with feelers adapted to contact the part in determined points and transducers adapted to detect the displacements of the arms; the transducers are connected to a processing unit that takes care of detecting and possibly combining the signals for obtaining the deviations of the part dimensions from pre-set nominal dimensions.
This type of apparatus is very fast and accurate, the scarcely flexible in its range of applications, because the heads are arranged according to a substantially rigid disposition, for the comparative checking of a determined type of part.
Another known apparatus, in particlar a coordinate measuring machine, is disclosed by British patent application No. 2112140.
Traditionally, coordinate measuring machines were used for applications in the quality control department, or anyway in departments different from the manufacturing shops.
The machine described in British patent application No. 2112140, that--on the contrary--is also intended for measurements in manufacturing shops, comprises a support structure, a system of three slides movable with respect to the support structure along three perpendicular axes, transducer means including incremental linear transducers adapted to detect the positions of the slides with respect to the support structure, measuring means constituted by a measuring head carried by one of the slides and having a feeler for performing measurements along said three perpendicular axes, control means comprising electric motors and driving devices for controlling the displacements of the slides according to a program, and processing means connected to the linear transducers and the measuring head for determining the dimensions of the part as a combination of the relevant signals of the linear transducers and the measuring head. The parts are transferred from the manufacturing line to a round table of the measuring machine, that can be differently oriented.
This coordinate measuring machine is evidently very flexible, since it may check parts of very different types, but is rather slow because, for example, checking a diameter requires at least two touches of the feeler. Moreover, in order to obtain accurate measurement it is indispensable that during the measurement cycle the part remain perfectly stationary, or anyway in exactly known positions with respect to the machine; to this end, as already mentioned, the part is taken away from the manufacturing line and is loaded onto the round table of the measuring machine.
If the machine were used for checking parts arranged in a manufacturing line, for example onto a pallet conveyor, possible settings or vibrations of the pallet, e.g. during the displacements of the slides necessary for subsequently bringing the feeler into contact with diametrically opposite points of a round part, might cause unacceptable errors.
To sum up, since in a coordinate measuring machine every dimension is measured by combining subsequent sequential measurements, each of which relating to a single point, the part positioning is a harshly critical factor.